| Abstrakt: |
Carbon-13 chemical-shift tensors measured in a single crystal of sucrose are assigned and interpreted. Two methods, local symmetry orientation and 13C-1H dipolar spectroscopy, are used to assign the tensors. A quantitative technique which uses the local symmetry environment of each carbon to assign tensors is described. The data are linearly fitted with tensors obeying the local symmetry for every possible assignment permutation, and that permutation which minimizes the sum of the squares of the distances from the model tensors to the measured tensors is taken as the most likely assignment. A 3D technique for obtaining dipolar spectra for individual carbons is described, and results are exhibited for each of the 24 magnetically nonequivalent carbons in the unit cell of sucrose. These two complementary methods are applied within three groups of tensors, sorted initially by their principal values, to assign with reasonable certainty all 24 tensors to the carbons in the two molecules in the sucrose unit cell. The assigned tensors are discussed in terms of the anomeric and exoanomeric effects and their relation to the local symmetry.Copyright 1993, 1999 Academic Press |
